Guest Author - William Charles Vetter

In 1986 I had a new BMW; at the time it was the absolute pinnacle of automotive innovation. I used to love taking people for rides and then demonstrate the amazing abilities of my new car’s ABS brakes. My favorite trick was to drive about 40 miles per hour and put the tires on the right side of the car close to the curb where there is almost always some loose sand. I would yell, “Hey watch this”, and then stomp on the brake pedal as hard as possible as I took my hands off of the steering wheel! Unsuspecting passengers would invariably gasp in terror and then laugh as the car would shudder, vibrate and then come to a straight and controlled stop without any sliding.

Arguably one of the most important safety developments of cars was the recent advent of the Anti-lock Braking System (ABS). First introduced in passenger cars in 1978 ABS has been around since the late 1920’s, originally developed for aircraft. ABS allows a central computer to monitor the speed of each wheel. Individual wheel sensors send speed data to a central computer which reduces the braking force to any wheel which slows more quickly than it should. The central Controller Antilock Brakes (CAB), makes constant brake pressure updates to each wheel at a rate of up to 20 times per second, thus reducing the likelihood of an uncontrolled slide. My 1986 Beemer had 4 channel Bosch ABS with a separate sensor on each individual wheel, essentially in my panic braking demonstration my right tires were allowed to roll at their maximum traction while the left wheels provided most of the stopping power. In my demonstration; if my car did not have ABS my reluctant spectator and I would have become a statistic in a classic rollover accident.

The tires under your car are at their best while they are rotating in concert with the road below. As you apply the brakes traction forces continue to climb up until the moment that the tires top rotating and lose concert with the road below, this causes the tires to now skid across the road surface, and as they do so, they become subject to dynamic attrition. In essence what ABS does—in an emergency, it ensures that the wheels don't lock up but instead keep spinning so that the tires maintain grip with the road.

Like most people, you might believe that ABS is designed to bring your car to a stop faster than a conventional braking system and in most situations this is true but the reality is that ABS was designed to allow you to maintain control of your cars steering under difficult braking situations. You cannot steer your car around an object if your tires are sliding and so ABS allows you to miss an obstruction while still braking hard. To take advantage of ABS you need to keep your wits about you and steer while braking hard. The instinctive action when slamming on the brakes is to lock your elbows straight and brace for an impact thus negating ABS biggest advantage—steering control under hard braking.

You will love your ABS most of the time but the time may come when you will absolutely hate ABS. ABS has several disadvantages and if you drive long enough you will eventually curse the very concept of ABS. In several conditions ABS will become a liability. If you are driving on snow, mud or a gravel road surface ABS will actually hinder your vehicles ability to come to a stop. On these unstable surfaces nothing can bring you to a stop faster than locking up your wheels, allowing your tires to build up small dams of material which will bring your car to a stop as the built up material creates a block to your forward progress. Allowing your wheels to continue rolling over these loose moveable surfaces will greatly increase your cars stopping distance. Unfortunately there is no way to disable your cars ABS, unlike traction control. I am not sure why this is but that’s just the way that it is.

These snow driving issues aside, a 2003 study shows that ABS has contributed to an 18% reduction in multi vehicle accidents and a whopping 35% drop in run-off-road accidents. I highly recommend ABS as possibly the most desirable of new car options unless of course you happen to spend most of your time driving on snow or mud.